Abstract This R34 study will first develop treatment quality assurance procedures designed to increase the adoption and quality of empirically supported family-based services (FBS) for adolescent substance use (ASU) in usual care, and then test two system-level implementation strategies for installing the new quality procedures in ASU treatment sites. FBS have achieved the strongest evidence base for treating ASU and are a prime candidate for upgrading the quality of ASU services in various systems of care. FBS comprise both family participation in services, the systemic parameters wherein family members are included in assessment and treatment activities; and family therapy techniques, the specific interventions that clinicians use to directly target family members and family functioning for change. For FBS to fulfill their potential to enhance ASU treatment systems, FBS implementation must be supported by effective quality assurance (QA) procedures designed to ensure that FBS are delivered with fidelity. To advance this effort, the proposed study will leverage a strong research-government partnership between the applicant organization and the New York single-state agency for SU services. The study will first develop innovative QA procedures (Aim 1) that use existing FBS quality metrics to promote high-fidelity FBS: Measurement Feedback System for Implementation (MFS-I), a pragmatic evidence-based method for increasing FBS quality by providing monthly feedback on therapist-reported FBS delivery along with brief online FBS training modules. The study will then experimentally compare two system- level implementation strategies designed to foster MFS-I utilization in usual care for ASU. Core Training Only will contain two 3-hour training sessions: Mapping existing FBS and identifying site goals for FBS improvement; and Installing and sustaining the MFS-I. Core + Facilitation is an additive strategy that will begin with the Core Training sessions and then continue with monthly facilitation meetings for one year to promote MFS-I use and progress toward FBS improvement. The study will feature a three-group cluster randomized trial testing Core Training Only versus Core + Facilitation versus no-intervention Control in 15 representative ASU clinics across New York State. MFS-I utilization data will be collected from Core Training and Core + Facilitation sites for one-year follow-up (after initial Core Training); FBS quality data on family participation and family therapy technique use will be collected from all sites over one-year follow-up; and client outcome data for all sites will be retrieved from administrative data warehouses over one-year baseline and one-year follow-up. These data will enable between-condition comparisons of FBS delivery (Aim 2: MFS-I utilization, family participation, family therapy technique use) and client outcomes (Aim 3: therapeutic goal achievement, substance use change). If study aims are achieved, investigators would be positioned to mount a fully powered RCT to test the effectiveness of these FBS quality improvement procedures at scale.